Method for Treating an Abrasive Article, and Abrasive Article

ABSTRACT

A method for treating an abrasive article includes applying a release agent dispersion onto at least one surface, which is provided for abrading, of the abrasive article in order to produce a cover layer. The release agent dispersion includes at least one anti-adhesion agent. The release agent dispersion further includes at least one film-forming agent.

The invention relates to a method for treating an abrasive article,where a release agent dispersion is applied at least to a surface of theabrasive article intended for grinding to produce a covering layer,where the release agent dispersion comprises at least one anti-adhesionagent. Furthermore, the invention relates to a corresponding abrasivearticle.

PRIOR ART

Methods for treating an abrasive article are already known, for examplefrom U.S. Pat. Nos. 5,766,277 B and 2,768,886 B, and in these a releaseagent dispersion is applied at least to the surface of the abrasivearticle intended for grinding to produce a covering layer, where therelease agent dispersion comprises at least one anti-adhesion agent.

DISCLOSURE OF THE INVENTION

The invention proceeds from a method for treating an abrasive article,in particular a coated abrasive article, where a release agentdispersion is applied at least to a surface of the abrasive articleintended for grinding to produce a covering layer, where the releaseagent dispersion comprises at least one anti-adhesion agent.

An “abrasive article” is employed for the grinding or abrasive workingof a workpiece, in which the material of the workpiece is mechanicallyremoved in the form of swarf from the surface of the workpiece. Theabrasive article is, in particular, a coated abrasive article. Theabrasive article comprises an abrasive article substrate, in particulara flexible abrasive article substrate, having at least one layer. Theabrasive article substrate can comprise, in particular, paper,paperboard, vulcanized fiber, foam, a polymer, a textile structure, inparticular a woven fabric, formed-loop knitted fabric, drawn-loopknitted fabric, braid, nonwoven, or a combination of these materials, inparticular paper and woven fabric, in one or more layers. The abrasivearticle substrate, in particular flexible abrasive article substrate,gives the abrasive article specific properties in respect of adhesion,elongation, tear strength and tensile strength, flexibility andstability. In a coated abrasive article, abrasive grains are fixed bymeans of a binder (often referred to as base binder) on the abrasivearticle substrate. By means of the binder, the abrasive grains are atleast prefixed, in particular fixed, in particular in a desiredorientation and/or distribution, on the abrasive article substrate. Aperson skilled in the art will know of suitable binders for fixingabrasive grains on the abrasive article substrate from the prior art.Such binders of the prior art are typically solvent-based adhesives suchas polychloroprene. In addition to the binder as base binder, it ispossible to use a further binder known as a covering binder which isapplied, in particular, as a layer over the abrasive grains which havebeen fixed by means of the base binder on the abrasive articlesubstrate. Here, the covering binder bonds the abrasive grains firmly toone another and firmly to the abrasive article substrate. Suitablecovering binders, in particular, will be adequately known to a personskilled in the art from the prior art. Possible covering binders are, inparticular, synthetic resins such as for example phenolic resin, epoxyresin, urea resin, melamine resin, polyester resin. In addition, furtheradditives (“grinding additives”) can be provided in order to give theabrasive article specific properties. A person skilled in the art willbe familiar with such additives.

Furthermore, alternative abrasive articles, such as for example bondedabrasive articles, are in principle also conceivable. Bonded abrasivearticles are, in particular, typically synthetic resin-bonded partingand grinding disks, with which a person skilled in the art will befamiliar. For synthetic resin-bonded parting and grinding disks, acomposition is produced by mixing abrasive minerals together withfillers, pulverulent resin and liquid resin and this is then pressed togive parting and grinding disks of various thickness and diameters. Inparticular, the parting and grinding disks also comprise woven fabriclayers composed of glass fibers. Curing of the composition typicallyoccurs at about 180° C. In combination with the method of the invention,advantages according to the invention can also be achieved in the caseof such abrasive articles.

The abrasive article has a surface intended for grinding, i.e. anabrasive surface, in particular on that side of the abrasive article onwhich the abrasive grains are fixed and optionally provided with acovering binder and/or a further additive. The abrasive surface of theabrasive article is moved over a workpiece to be worked during agrinding operation, so that a grinding effect is produced by theabrasive grains arranged on the abrasive surface. The abrasive articlecan in principle be present in various manufactured forms, for exampleas grinding disk or as grinding belt, as sheet, roller, strip or asabrasive article stock strip (e.g. in production).

The term “release agent dispersion” which is applied to the surfaceintended for grinding of the abrasive article refers to, in particular,a lubricant dispersion. The release agent dispersion is employed forapplication of materials present in the dispersion to the surface of theabrasive article, with these materials being present as fine,essentially insoluble particles in the dispersion medium (also:dispersion agent) of the release agent dispersion. In one embodiment,the release agent dispersion comprises water as dispersion medium. In analternative embodiment, the dispersion medium can also be formed byethanol, alcohol, an organic solvent or the like. The release agentdispersion is intended to be applied to the surface of the abrasivearticle and bring about formation of a covering layer on the surface.

The release agent dispersion comprises at least one anti-adhesion agent,in particular as material present in the dispersion medium. Here, an“anti-adhesion agent” is an agent which prevents or reduces accumulationof swarf formed during a grinding operation. The anti-adhesion agentserves to prevent or reduce accumulation of swarf in the intermediatespaces between adjacent abrasion grains, which can lead, in particular,to blocking or clogging of the abrasive surface of the abrasive article.In particular, the anti-adhesion agent serves to prevent or reduce theeffect in which swarf sinters together, sticks together or meltstogether under the action of the heat arising in a grinding process andmelts on the abrasive surface of the abrasive article and in this waylikewise leads to blocking or clogging of the abrasive surface of theabrasive article (as is often the case for, for example, polymers,polymer surface coatings or the like to be abrasively treated). In thisway, a cutting capability and in particular an operating life (servicelife) of the abrasive article is advantageously improved. In this way,the anti-adhesion agent serves as a type of lubricant between abrasivearticle and workpiece surface to be worked during a grinding operation.In particular, such an anti-adhesion agent is often referred to as“stearate” in the literature about abrasive articles, even though it cancomprise any materials which are useful for preventing the accumulationof swarf. For example, the anti-adhesion agent can comprise metal saltsof fatty acids (for example zinc stearate or calcium stearate), salts ofphosphate esters (for example potassium behenyl phosphate), phosphateesters, urea-formaldehyde resins, waxes, mineral oils, crosslinkedsilanes, crosslinked silicones, fluorinated chemicals and/orcombinations thereof as constituent. Such anti-adhesion agents are oftenproduced from fats in which a mixture of fatty acids is present. Forexample, an anti-adhesion agent—which is referred to as “stearate” inthe literature—can also contain calcium salts of other fatty acids, forexample palmitate, myristate or laurate. It is pointed out that suchanti-adhesion agents are known to a person skilled in the art, forexample from U.S. Pat. No. 5,766,277 B. The anti-adhesion agenttypically does not dissolve in the dispersion medium of the releaseagent dispersion (for example water), so that a release agent dispersioncontaining the anti-adhesion agent is present. In this case,anti-adhesion agent particles, in particular very fine anti-adhesionagents particles, “float” in the dispersion medium of the release agentdispersion. In this sense, the anti-adhesion agent or the anti-adhesionagent particles is/are present as fine, essentially insoluble particlesin the dispersion medium of the release agent dispersion.

According to the invention, the release agent dispersion comprises atleast one film-forming agent, in particular a filming agent and/or a gapfilling agent. According to the invention, the film-forming agent can beutilized to treat an abrasive article in such a way that no strips orstreaks remain on its surface as residue of a coating with theanti-adhesion agent.

A “film-forming agent” refers to a substance which is suitable and is inparticular also provided for producing bonding of individualanti-adhesion agent particles to the surface of the abrasive articleand/or to close gaps between individual anti-adhesion agent particles onthe surface of the abrasive article. This makes it possible to produce alayer, in particular uniform layer, or a film, in particular uniformfilm—the covering layer according to the invention—from the manyindividual anti-adhesion agent particles applied to the surface of theabrasive article. The covering layer advantageously no longer hasindividual anti-adhesion agent particles capable of refraction of light.In other words, no light-refracting residues which lead—depending on theposition on the surface of the abrasive article—to a nonuniform orinhomogeneous appearance (such as for example streaks or strips on thesurface) remain on the surface of the abrasive article after carryingout the method of the invention. Thus, a uniform covering layer whichappears optically transparent (or in some cases also translucent)through to optically slightly opaque is produced on the surface of theabrasive article. In particular, a covering layer having—depending onthe position on the surface of the abrasive article—a uniform orhomogeneous refractive index is made possible.

On the basis of present-day knowledge, the production of a uniform filmwhich appears optically transparent through to optically slightly opaqueappears to be possible by means of partial dissolution and joining ofneighboring anti-adhesion agent particles and/or by filling-up of gapsbetween neighboring anti-adhesion agent particles. A film-forming agentwhich brings about partial dissolution and joining of (two or more)neighboring anti-adhesion agent particles will in the context of thepresent text be referred to as “filming agent”. In particular, thefilming agent brings about adhesive bonding and filming (i.e. filmformation) of adjacent anti-adhesion agent particles. In particular,this partial dissolution, joining, adhesive bonding (may also becharacterized as melting) and/or filming of adjacent anti-adhesion agentparticles is made possible at advantageously low temperatures in therange from 0° C. to 100° C., in particular from 15° C. to 80° C., veryparticularly from 30° C. to 60° C. The filming agent thus acts in amanner analogous to an adhesive which partially dissolves the materialsof objects to be joined in the surface region and subsequently dries. Asa distinction from a filming agent, a film-forming agent which bringsabout the filling of gaps between neighboring anti-adhesion agentparticles will be referred to as “gap filler”. A gap filleradvantageously has a refractive index similar to that of theanti-adhesion agent particles, so that no or only very little refractionof light occurs at the places filled with gap filler between adjacentanti-adhesion agent particles and the gap filler thus likewise serves toproduce an optically transparent (or sometimes also translucent) buthomogeneous covering layer.

In one embodiment of the method, the film-forming agent comprises atleast one constituent which is suitable for partially dissolvinganti-adhesion agent particles. The constituent can, for example, beselected from a list, where the list comprises at least organic acids,alcohols, amines, phosphanes, lactic acid, acetic acid, salts of lacticacid, salts of acetic acid, in particular ammonium salts of lactic acid(ammonium lactate) or ammonium salts of acetic acid (ammonium acetate),polyethylenimine, polyethylene glycol, urea and mixtures thereof.Polyethylenimine in particular has good properties as film-formingagent, in particular as filming agent, since it becomes solid and doesnot diffuse after treatment of the abrasive article, in particular doesnot diffuse into the abrasive article. Polyethylene glycol has beenfound to be an advantageous gap filler. Urea, which is partiallydissolved by one of the abovementioned film-forming agents, is likewisesuitable as good gap filler.

In an embodiment of the method, the release agent dispersion contains atleast one surfactant. Surfactants which are able to achieve goodleveling, i.e. good spread, of the release agent dispersion on thesurface of the abrasive article while the abrasive article is beingtreated in the method of the invention are particularly suitable. Asurfactant leads to an advantageous equalization of amounts of releaseagent dispersion applied to the surface if the release agent dispersionis not applied homogeneously over the surface (self-leveling). Thisequalization occurs by flow of the release agent dispersion.

In an embodiment of the method, the release agent dispersion is appliedto the surface of the abrasive article at a temperature of the abrasivearticle in the range from 0° C. to 100° C., in particular from 15° C. to80° C., very particularly from 30° C. to 60° C. In particular, atemperature of above 0° C. leads to evaporation of the dispersion mediumwater, with the anti-adhesion agent and the film-forming agent remainingon the surface of the abrasive article—where a gap filler fills gapsbetween anti-adhesion agent particles and/or a filming agent partiallydissolves and joins adjacent anti-adhesion agent particles—and theoptically homogeneous covering layer being formed in this way. Thehigher the temperature selected, the more quickly does evaporation ofthe dispersion medium occur. On the other hand, heating of the abrasivearticle to a high temperature is costly and complicated in terms ofmanufacturing technology. In one embodiment of the method, the releaseagent dispersion is applied to the surface of the abrasive articleduring the production process of the abrasive article, in particularafter a process step of heating the abrasive article, very particularlybefore a process step for cooling the abrasive article. Accordingly, itis sufficient in order to maintain the proposed temperatures to treatthe abrasive article in the still-hot state during or immediately aftermanufacture thereof—during which heating to typically above 70-140° C.is carried out in order to cure the binder. Here, heating means heatingof the abrasive article to significantly above room temperature, i.e.above 30° C., in particular above 50° C., very particularly above 70° C.According to the invention, residual heat still present in the abrasivearticle can be utilized and it is not necessary to reheat the abrasivearticle in a heating oven in a (further) process step ofafter-treatment. Here, “production process” means the sequence ofprocess steps which serve to manufacture and provide the abrasivearticle. In an embodiment, these process steps can be formed by (1)application of base binder to an abrasive article substrate, (2)sprinkling of abrasive grains onto the abrasive article substratecovered with base binder, (3) curing of the base binder, (4) applicationof a covering binder, (5) drying and/or curing of the resulting abrasivearticle by heating of the abrasive article, (6) cooling of the abrasivearticle and (7) finishing (stamping or laser cutting) of the abrasivearticle. According to the invention, the release agent dispersion can beapplied to the surface of the abrasive article during the productionprocess of the abrasive article, in particular after the process step(5) of heating to effect drying and/or curing of the abrasive article(also: drying process step), very particularly before the coolingprocess step (6) for the dried/cured abrasive article and the residualheat present in the abrasive article can be utilized in this way.Furthermore, the method of the invention can be integrated in this wayinto an existing process chain of the production process and acorresponding process facility, for example into an existingmanufacturing plant, without further, in particular complicated,machines or restructuring being necessary in the process chain and/orprocess facility. In particular, no separate heating oven is thereforerequired and/or no double utilization of an existing heating oven fordrying/curing (in process step (5)) and for later reheating in order totreat the abrasive article is necessary for carrying out the method. Inone embodiment, the release agent dispersion can be applied directly“in-line” onto an abrasive article stock strip (referred as stock strip)moving through a manufacturing plant and which has previously beenheated for drying and curing of the binder, with the dispersion mediumwater of the release agent dispersion evaporating and filming of thesurface occurring to form the covering layer.

Furthermore, the covering layer produced by application of the releaseagent dispersion to the surface of the abrasive article can be dried inthe process step for cooling the abrasive article by means of an airstream in such an embodiment of the method. Here, the cooling effectexerted on the abrasive article is reinforced and drying of the coveringlayer is at the same time accelerated.

The release agent dispersion can be applied to the surface of theabrasive article by means of doctor blade coating, rolling-on, printing,brushing or the like. In one embodiment of the method, the release agentdispersion is applied to the surface of the abrasive article by means ofpulsed spraying. Pulsed spraying—i.e. repeated spraying with briefinterruptions (intermittent spraying)—assists metering because thepressure and, associated therewith, droplet formation of the releaseagent dispersion applied to the surface of the abrasive article remainconstant. Furthermore, the amount of release agent dispersion sprayed oncan be altered in a simple way by varying the opening time of the sprayvalve (for example by changing the opening time from 10 milliseconds to50 milliseconds per impulse). In particular, an otherwise necessarycleaning of adhesive boat and application roller(s) can be avoided inthe cleaner process operation of spraying compared to a rolling of asolution onto the surface of the abrasive article as is known from theprior art.

In an embodiment of the method, the release agent dispersion has asolids content in the range from 20% to 60%, in particular from 25% to50%, very particularly from 30% to 40%. The values according to theinvention are advantageous solids contents for processing the releaseagent dispersion. A particularly high solids content makes it possibleto achieve a high density of anti-adhesion agent particles sprayed onthe surface of the abrasive article. On the other hand, a low solidscontent (i.e. a low-viscosity or fluid property) allows particularlygood meterability and processability by means of the spray valves (spraynozzles), because these do not block. Furthermore, a release agentdispersion having a low solids content which has been sprayed onto thesurface can distribute more readily on or over the surface (by flowing).In one embodiment, the solids content can be 33%.

The invention also provides an abrasive article which has been treatedby a method according to the invention.

DRAWINGS

The invention is explained in more detail in the following descriptionon the basis of embodiments depicted in the drawings. The drawings, thedescription and the claims contain numerous features in combination. Aperson skilled in the art will also advantageously look at the featuresindividually and assemble them to give useful further combinations.Identical reference numerals in the figures denote identical elements.

The figures show:

FIG. 1 a part of an illustrative embodiment of an abrasive articleaccording to the invention with abrasive grains in a schematic sectionalview;

FIG. 2 a process flow diagram for depicting the method of the inventionfor treating an abrasive article;

FIG. 3 a process flow diagram for depicting an illustrative integrationof the method of the invention as per FIG. 2 into a manufacturingprocess for an abrasive article.

FIG. 1 shows a part of an illustrative embodiment of an abrasive article10 according to the invention with abrasive grains 12 in a schematicsectional view. In the embodiment depicted, the abrasive article 10 is acoated abrasive article 10 having an abrasive article substrate made ofvulcanized fiber. The abrasive article substrate 22 made of vulcanizedfiber serves as flexible substrate for the abrasive grains 12.Vulcanized fiber is a composite material composed of cellulose, inparticular cotton or cellulose fibers, and is adequately known to aperson skilled in the art as flexible substrate for abrasive articlesfrom the prior art. The abrasive grains 12 are fastened by means of abinder 20, in particular a base binder 24, in the form of, for example,phenolic resin, to the abrasive article substrate 22. The layer of basebinder 24 and abrasive grains 12 is additionally coated with a coveringbinder 26 (the covering binder 26 likewise represents a binder 20), inparticular likewise composed of phenolic resin.

The abrasive article 10 has been treated by the method according to theinvention for treating an abrasive article 10, by a further coveringlayer 30 being applied to the surface 28 intended for grinding of theabrasive article 10. The application of the covering layer 30 is carriedout by use of the method 100 according to the invention, cf. FIG. 2.

FIG. 2 shows a process flow diagram to depict an embodiment of themethod 100 according to the invention for treating an abrasive article10, with a release agent dispersion for producing a covering layer 30being applied to at least one surface 28 of the abrasive article 10 inthe treatment of the abrasive article 10.

In a first method step 102, a release agent dispersion comprising atleast one anti-adhesion agent is provided. In this embodiment, therelease agent dispersion further comprises a surfactant. This releaseagent dispersion here comprises, for example, water as dispersionmedium, a stearate, in particular a calcium stearate, as anti-adhesionagent. The release agent dispersion here has a solids content in therange from 30% to 40%, for example 35%.

In method step 104, the release agent dispersion provided is admixedwith at least one film-forming agent. Admixing is carried out, inparticular, by blending or stirring the mixture of release agentdispersion and film-forming agent. The film-forming agent comprises, inparticular, a filming agent and/or a gap filler. In an embodiment, thefilm-forming agent is a mixture of lactic acid and polyethylene glycol.In method step 106, the release agent dispersion which has been admixedwith the film-forming agent is applied to the at least one surface 28 ofthe abrasive article 10. Application is carried out in this embodimentby pulsed spraying onto the surface 28 of the abrasive article 10 usingat least one atomizer nozzle (not shown in more detail here). The pulsedspraying is carried out here by repeated intermittent spraying at anaverage frequency of 20 Hz, with valve opening times of about 20milliseconds.

FIG. 3 shows a process flow diagram to depict an exemplary integrationof the method 100 according to the invention as per FIG. 2 into amanufacturing process 200 for an abrasive article 10. The manufacturingprocess 200 comprises at least the following process steps.

In process step 202, an abrasive article substrate 22, for examplecomposed of vulcanized fiber, is provided. In process step 204, a basebinder 24 is applied to the abrasive article substrate 22, for exampleby doctor blade coating or rolling-on. In process step 206, abrasivegrains are sprinkled, for example by means of electrostatic sprinklingas is known from the prior art, onto the abrasive article substrate 22which has been covered with base binder. In process step 208, the basebinder 24 is firstly cured and subsequently coated in process step 210with a covering binder 26, in particular by rolling-on or brushing-on.In process step 212, the abrasive article 10 obtained in this way isdried/cured (in particular the covering binder 26 is also cured) byconveying it through a heating oven and thus heating it. The heatingoven is, for example, heated to 120° C. In parallel to these processsteps 202 to 212, the method steps of the method 100 according to theinvention can be carried out, in particular carrying out the methodsteps 102 to 104, as depicted in FIG. 3 (as an alternative, these methodsteps 102 to 104 can also be carried out before or after the processsteps 202 to 212 are carried out). After heating and drying/curing theabrasive article 10 in process step 212, the release agent dispersion isapplied to the surface 28 intended for grinding of the abrasive article10 in process step 214, i.e. method step 106 of the process of FIG. 2 iscarried out. At this point in time, the release agent dispersioncomprises at least one anti-adhesion agent and a film-forming agent,optionally a surfactant. At the point in time of application of therelease agent dispersion, the abrasive article 10 has a temperature ofabout 50° C. As described, application is carried out by means of pulsedspraying (cf. above in respect of method step 106). The covering layer30 produced by application of the release agent dispersion to thesurface 28 of the abrasive article 10 is dried by means of an air streamin a process step 216 for cooling (cooling process step) the still hotabrasive article 10, with the still hot abrasive article 10 being cooledat the same time and the dispersion medium water of the release agentdispersion applied to the surface evaporating at the same time. As aresult of the residual heat, the film-forming agents, i.e. the gapfiller and the filming agent, react and form an optically homogeneous,i.e. streak-free, covering layer. Finally, the abrasive article 10obtained in this way can be finished, for example by stamping or lasercutting, in process step 218.

1. A method for treating an abrasive article, comprising: applying arelease agent dispersion at least to a surface of the abrasive articlein order to produce a covering layer, wherein the surface is configuredfor grinding, wherein the release agent dispersion comprises at leastone anti-adhesion agent, and wherein the release agent dispersionfurther comprises at least one film-forming agent.
 2. The method asclaimed in claim 1, wherein the release agent dispersion furthercomprises at least one surfactant.
 3. The method as claimed in claim 1,wherein applying the release agent dispersion comprises: applying therelease agent dispersion to the surface of the abrasive article at atemperature of the abrasive article in a range from 0° C. to 100° C. 4.The method as claimed in claim 1, wherein the release agent dispersionhas a solids content in a range from 20% to 60%.
 5. The method asclaimed in claim 1, wherein applying the release agent dispersioncomprises: applying the release agent dispersion to the surface of theabrasive article using pulsed spraying.
 6. The method as claimed inclaim 1, wherein applying the release agent dispersion comprises:applying the release agent dispersion to the surface of the abrasivearticle during a production process for the abrasive article, after aprocess step for heating the abrasive article, and before a process stepfor cooling the abrasive article.
 7. The method as claimed in claim 1,further comprising: drying the covering layer using an air stream in aprocess step for cooling the abrasive article.
 8. An abrasive article,comprising: a surface configured for grinding, a covering layerconfigured to cover the surface, the covering layer formed by applying arelease agent dispersion to the surface, the release agent dispersioncomprising (i) at least one anti-adhesion agent, and (ii) at least onefilm-forming agent.
 9. The abrasive article as claimed in claim 8,wherein the film-forming agent is a filming agent and/or a gap filler.10. The abrasive article as claimed in claim 1, wherein the film-formingagent is a filming agent and/or a gap filler.